According to Alice Hughes, a researcher with the Chinese Academy of Sciences’ Centre for Integrative Conservation, global analyses often underestimate levels of deforestation driven by road-building in the Indo-Malaysia region. This is because many of those analyses rely on a widely used global map of roads compiled by Open Street Maps (OSM) that misses as much as 99 percent of roads in parts of the region.

According to Hughes, this level of inaccuracy can have serious consequences: “Not only does it mean that any analysis based on global roads datasets will underestimate the level of fragmentation and overestimate the forest coverage of a region, but most forms of exploitation also occur within close proximity to a road.”

Increasing deforestation is not the only threat posed by opening new areas to roads. “These growing road networks provide accessibility for other forms of resource exploitation,” Hughes notes in the study. “Most notably this includes selective logging, and hunting, which in the Indo-Malay region also targets a vast suite of species as pets, medicine and meat.”

Southeast Asia is a global biodiversity hotspot, and Indonesia and Malaysia are no exception, harboring some of the highest levels of species diversity in the world. Yet those two countries also supply more than 80 percent of the world’s palm oil, and it’s widely acknowledged that the expansion of oil palm plantations in the Indo-Malaysian region has led to massive deforestation, imperiling biodiversity.

Now, new research suggests that the deforestation threats facing the region may be drastically under-appreciated.

According to Alice Hughes, a researcher with the Chinese Academy of Sciences’ Centre for Integrative Conservation, global analyses often underestimate levels of deforestation driven by road-building in the Indo-Malaysia region. This is because many of those analyses rely on a widely used global map of roads compiled by Open Street Maps (OSM) that misses as much as 99 percent of roads in parts of the region.

Because national road maps are not openly available for Indonesia and Malaysia, Hughes used high-resolution imagery data to manually map the roads in 149 plots, each 1,866 square kilometers in size, spread across the Indo-Malaysian region in such a way as to provide a representative sample of the region as a whole. She then compared her road map to a composite OSM road map for the region. Her findings are detailed in a study released earlier this month by the journal Biological Conservation.

“The percentage of roads mapped within the OSM database varies dramatically across the region, with 70.6% of districts showing over 75% of roads unmapped, and almost 24% of districts showing 95–100% of roads unmapped,” she writes in the study. “At a country level Malaysia shows the lowest percentage of roads mapped with 89% of roads in Sabah and Sarawak currently unmapped, which though worse than Indonesia’s 70.2% is comparable to that of Kalimantan (87%). The Solomon islands and PNG are only marginally better at 73.9% and 64% unmapped respectively.”

According to Hughes, this level of inaccuracy can have serious consequences. “Not only does it mean that any analysis based on global roads datasets will underestimate the level of fragmentation and overestimate the forest coverage of a region, but most forms of exploitation also occur within close proximity to a road,” she said in a statement provided to Mongabay.

A logging road cuts through the forest in Sabah, Malaysia. Photo by Rhett Butler.

Using recent deforestation data, Hughes was able to determine that more than 99 percent of all deforestation in Sabah occurs within 2.5 kilometers of a road. In 55.6 percent of the entire Indo-Malaysia region, in fact, the rate of road-adjacent forest destruction is only slightly lower than it is in Sabah, with more than 90 percent of all deforestation occurring within that same distance of the nearest road. “Overall 87% of deforestation is within 2.5 km of a road, 74% within 1 km and 60% within 500 m,” Hughes writes in the study.

This is worrisome, she adds, given that about 44 percent of the entire region is within 2.5 kilometers of a road, and the average distance to the nearest road across the region dropped from 21.34 kilometers to just 6.28 kilometers once all roads were factored in.

Increasing deforestation is not the only threat posed by opening new areas to roads. “These growing road networks provide accessibility for other forms of resource exploitation,” Hughes notes in the study. “Most notably this includes selective logging, and hunting, which in the Indo-Malay region also targets a vast suite of species as pets, medicine and meat. The increasing access to formerly inaccessible forest may be devastating for many species.”

Bill Laurance, a tropical ecologist at Australia’s James Cook University, told Mongabay that “The results of this study are as simple as they are scary. First, roads are overwhelmingly the main predictor of deforestation in the Indo-Malaysian region. It’s a slam-dunk effect, completely off the charts statistically. If you want to know where deforestation has happened or is going to happen, just map out all the roads.”

He added: “Second, in developing nations like those studied here, we don’t know where most of the roads are located, even using our best technology and datasets. In Indonesia, 70% of the roads don’t appear on any map or dataset. In Malaysia, it’s 90%. Numbers like these should keep us all awake at night, worrying about roads.”

Past studies have also shown “the pervasive impact of roads on tropical systems via various secondary phenomena,” Hughes writes in Biological Conservation, “from increasing probability of invasion by non-native species, to microclimatic and hydrological changes, fire-risk, ease of access for other forms of development and exploitation, and of course roadkill.”

Hughes writes that protected area coverage in the Indo-Malaysia region is so lacking that there is an urgent need to designate new protected areas that better cover regional biodiversity. Asian wildlife is already bearing the brunt of road-building, as she points out: “One of the best documented consequences of the development of roads through forested landscapes is the ability to exploit wildlife populations, and much of Asia already has few mammals of over 2 kg outside protected areas as a direct result of overexploitation; which is of course facilitated by greater access.”

A logging truck carrying timber out of the Malaysian rainforest. Photo by Rhett Butler.